Human Tissue Types and Biological Functions

Understanding Biological Tissues

Tissue: A tissue is a collection of cells of the same type, with a very similar structure that performs the same functions.

Epithelial Tissue

Epithelial tissue is composed of cells that are very close together, often having geometric shapes and appearing together forming units or layers. Two groups are distinguished:

• Surface epithelium: This covers and protects external surfaces or internal cavities of the organism. Notable examples include: the mucous lining of the oral cavity, pharynx, and esophagus; the endothelium lining the inside of blood vessels; and the heart epithelium.
• Glandular tissue: This is the way glands are formed. Its function is to secrete substances. They are distinguished as:
  • Exocrine Glands: If the substances produced are discharged to the outside or inside of body cavities.
  • Endocrine Glands: If the substances produced are hormones and are released into the blood.
  • Mixed Glands: These act as both exocrine and endocrine glands at the same time.

Connective Tissue

Connective tissue consists of cells embedded in a specialized intercellular substance with fibers. It is divided into:

• Connective tissue proper: This lies between other tissues and between organs, uniting them (such as tendons, ligaments, etc.).
• Adipose tissue: This is characterized because its cells, called adipocytes, are full of fat. Its function is the protection and maintenance of lipid reserves for some organs.
• Cartilage: Formed by cells called chondrocytes, which produce a more or less solid intercellular substance.
• Bone Tissue: Composed of cells called osteocytes, which are responsible for developing a strong intercellular substance.

Muscular Tissue

Muscular tissue consists of elongated cells called muscle fibers that contain fibrillar proteins (actin and myosin, which are responsible for muscle contraction and relaxation). Three types are distinguished:

• Smooth muscle tissue: Consists of elongated cells with one nucleus, and its contraction is involuntary.
• Striated muscle tissue: This is composed of cells with many nuclei.
• Heart muscle tissue: This is composed of cells with a striated appearance and a single nucleus, joined together in a network, and its contraction is involuntary.

Nervous Tissue

Nervous tissue detects changes in the external and internal environment and transmits orders throughout the organism. It is distinguished by:

• Neurons: Tree-shaped cells that present a cell body, dendrites, and an axon. Their function is to transmit nerve impulses.
• Glial cells (glia): These are non-neuronal cells that accompany neurons. Their functions are to protect and nourish neurons.